The present invention relates to a measuring circuit of an electronic clinical thermometer which utilizes a temperature characteristic of the quartz vibrator.
It is well known that the oscillating frequency of a quartz vibrator changes with a change in temperature, and a so-called electronic clinical thermometer has been proposed which has a first oscillator whose oscillating frequency is relatively stable over a wide temperature range, a second oscillator whose oscillating frequency is largely changeable according to a temperature change, means for dividing in frequency the output signal of the first or second oscillator to obtain a gate pulse signal, and a frequency counter which counts the oscillating frequency of the other oscillator by the use of the gate pulse signal.
An object of the present invention is to provide an electronic clinical thermometer which is able to hold the maximum body temperature as well as the conventional mercury clinical thermometer.
The present invention will be described in more detail in conjunction with the drawings.
FIG. 1 is a graph illustrating the relationship between an oscillating frequency and the temperature of the quartz vibrator used as a temperature sensor. In the manufacturing process of a quartz vibrator, when the vibrator is cut with a predetermined angle, it is possible to theoretically obtain a quartz vibrator having a turning point of -290.degree. C. approximately. When the vibrator is used between 0.degree. C. and 50.degree. C., the end portion of a second degree curve indicating the temperature characteristic has the characteristic that large changes in frequency will be caused by small changes in temperature (shown by the curve section A in FIG. 1).
The principle of the measurement of an electronic clinical thermometer is that the large change in frequency is applied to a thermosensor, and FIG. 2 is an enlarged figure of the curve section A of FIG. 1. In FIG. 2, the rate of the frequency change is approximately 50 PPM/.degree.C.